About 20% of MS patients use cannabis, and preliminary evidence suggests smoked cannabis may worsen the processing speed and memory deficits that MS itself causes.
Read this if you have MS and use cannabis, and are concerned about its effects on your thinking.
~20% of MS patients use cannabis; cognitive effects poorly studied
What the researchers found
This review examined the sparse literature on cannabis effects on cognition in people with multiple sclerosis. About 20% of MS patients use cannabis for symptom relief or as a lifestyle choice. Since MS itself impairs cognition in many patients, the question of whether cannabis adds to that impairment is clinically important.
The limited evidence available suggested that smoked cannabis may further compromise information processing speed and memory in MS patients. Brain imaging (fMRI) showed more inefficient cerebral activation patterns during cognitive tasks in MS patients who use cannabis compared to those who do not.
Findings for pharmaceutical cannabis preparations (capsules or spray) were mixed and inconclusive. The authors emphasized that the evidence was preliminary due to methodological limitations and the small number of studies.
Why it matters
MS patients face a difficult trade-off: cannabis may help with spasticity and pain but could worsen cognitive function. Without clear data, patients and clinicians are making decisions in the dark. This review highlights the urgent need for dedicated research.
The numbers in context
About 20% of MS patients use cannabis. Smoked cannabis associated with slower processing speed and poorer memory. fMRI showed less efficient brain activation patterns. Pharmaceutical cannabis findings were equivocal.
How the study worked
Narrative review of existing literature on cannabis effects on cognition in MS patients, including both smoked cannabis and pharmaceutical preparations. Coverage included behavioral cognitive testing and fMRI brain imaging studies.
What this study cannot tell us
Very few studies available for review. Methodological limitations in existing research (small samples, cross-sectional designs, confounders). Cannot determine whether observed cognitive differences are caused by cannabis or reflect pre-existing differences between users and non-users.
How to read the evidence
Narrative review of a very small evidence base. Findings are preliminary and based on studies with methodological limitations.
When this study was published
Published in 2015. Research on cannabis and cognition in MS has expanded since.
The bigger picture
Cannabis is increasingly recommended or self-prescribed for MS symptoms, but its cognitive effects in a population already dealing with cognitive decline are poorly studied. This represents a significant gap in the evidence base for MS treatment guidelines.
Questions still open
- Does the form of cannabis (smoked vs. pharmaceutical) matter for cognitive effects in MS? Would lower-dose or CBD-dominant preparations avoid cognitive impairment? Do the cognitive costs outweigh the symptomatic benefits for individual patients?
Common questions
Does cannabis worsen thinking problems in MS?
Should MS patients avoid cannabis?
Read the original research
What to make of cannabis and cognition in MS: In search of clarity amidst the haze.
Multiple sclerosis (Houndmills, Basingstoke, England), 21(14), 1755-60
Citation
Feinstein, Anthony; Banwell, Emma; Pavisian, Bennis. (2015). What to make of cannabis and cognition in MS: In search of clarity amidst the haze.. Multiple sclerosis (Houndmills, Basingstoke, England), 21(14), 1755-60. https://doi.org/10.1177/1352458515607652
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